Specifying the Time Period for Which to Display Statistics
In the Real-Time: Last Hour mode, the data in the Performance Hub is sourced from
Active Session History (ASH). The ASH data is written to disk when the ASH buffer is
filled up or after 1 hour, and is stored as part of the AWR framework.
By default, AWR has a retention period of 8 days. When you view historical data in
the Performance Hub, you are viewing statistics collected as part of the hourly
snapshots in AWR.
You use the Select Time Period field in the Performance Hub to determine the time
periods for which statistics are available for viewing. Because Oracle Database
statistics are stored in memory for one hour, the Real Time - Last Hour option always
appears in the Select Time Period list.
The historical data options that are available in the Select Time Period list change,
depending on the time period for which data is available in AWR, as shown in the
... zobacz całą notatkę